1. Field of the Invention
This invention relates to a backlight apparatus and a light guide plate used for a liquid crystal display (LCD) and the like, and particularly to an improved backlight apparatus and light guide plate provided with an element for a better light diffusion on a front surface or a back surface.
2. Prior Art
Among popular backlight systems of these days, a main current light guide is as shown in FIG. 33.
FIG. 33 shows an exploded state of a backlight apparatus adopting a conventional light guide system.
In FIG. 33, a light guide plate 1 is made of a light guide material such as a synthetic resin. The light guide plate 1 has a light emitting surface 1a and a back surface 1b which is opposed and inclined to the emitting surface 1a. Namely, the light guide plate 1 is made of a synthetic resin such as an acrylic resin or a polycarbonate, and generally has a wedge form. A dot print is provided on the back surface 1b to heighten light emission efficiency. A light source 2 is made of a thin tube of fluorescent lamp. The light source 2 is disposed to a thicker side of the light guide plate 1. A light diffusing film 3 is made of a frosted glass color film material to further diffuse the light from the light emitting surface 1a. A lens film 4 is composed of a lower lens film 4a and an upper lens film 4b. The lens film 4 serves to give a directivity to diffused light from the diffusing plate 3.
Such backlight apparatus operates as follows. The light from the light source 2 repeats diffusing and reflecting inside the light guide plate 1, and emitted from the emitting surface 1a thereafter. The light is given a uniform luminance or irradiance by the dot print provided on the back surfaced 1b. Moreover, the lens film 4 improves the directivity of the light so that the backlight apparatus has a predetermined directivity.
The backlight apparatus described above is complicated to assemble. Moreover, such backlight apparatus is expensive because it needs many parts. Japanese Laid Open Patent Publication No. 7-20466 proposes an improved apparatus to simplify assembling work, lessen the number of parts and make the outgoing light uniform.
FIG. 34 shows a backlight apparatus shown in Japanese Laid Open Patent Publication No. 7-20466. In FIG. 34, the same reference numerals and marks indicate the elements same as or corresponding to those of the conventional apparatus of FIG. 33, and their description is omitted.
In FIG. 34, a prism array 1c is provided on the light emitting surface 1a. The prism array 1c is integrally formed as a part of the light guide plate 1. Such prism array 1c distributes the light from the emitting surface 1a in the backlight apparatus.
However, in case the prism array 1c is provided on the light emitting surface 1a, the light directivity is oriented in one direction. Then, a lens sheet is required to correct it, actually. Therefore, such art is not so effective for decreasing the number of parts.